1. Field of the Invention
This invention relates to electric hair dryers and more particularly to a combination switch and variable control therefor which provides smooth continuous fan speed and heat adjustment while insuring the heat cannot be set too high without the fan being proportionately set to prevent over-temperature.
2. Description of the Prior Art
Various types of hand-held dryers of different wattages have come into vogue. These are generally classified as purse-type styling, or pistol-type dryers. The prime difference is in the overall shape since each is used for drying and styling the hair. Generally, the dryers have a blower and heater assembly to direct hot air stream over the hair as it is combed or brushed and they may have various attachments to style the hair while drying. The dryers include motor-driven fans of the cross-flow, centrifugal, or tangential type, and usually include a form of heater support or box structure mounting plural wattage heaters of coil resistance wires across the fan stream downstream thereof. Normally, thermostat means is disposed in the air flow to sense temperature rise of the air due to varying causes such as fan blockage, exit air blockage, or heat rises caused by frictional obstructions of one sort or another. On an over-temperature condition, the thermostat disconnects the heaters and shuts either the entire system down or the heater system permitting the fan motor to continue for cooling purposes. In such dryers it is desirable for the user to be able to adjust the amount of air flow and the amount of heat for different hair styling and drying conditions and thus vary both the speed and heat of the dryers. In currently available dryers, these two variables of speed and heat are controlled in generally two ways: first, by switch action in which independent or interconnected switching structure is used; or second, the variables may be controlled by electronic circuitry. The switch method is the most common but is usually limited to a few discrete operating points and the number of speeds and heats available are not always adequate for all drying and styling conditions. The electronic control overcomes this limitation by making the adjustment variable over some range of speeds and heats, but its disadvantage is the complexity and cost of the circuitry needed to control the variables especially on high wattage dryers. Neither the switch method nor the electronic control method usually gives independent control of speed and heat without considerable added cost and complexity and normally one control discretely changes both speed and heat together. Further, both 120 volt AC systems or lower voltage DC motors may be used. In the DC case it is common to obtain correct motor voltage by connecting resistance in series with the motor, the resistance consisting of low wattage heaters which thus serve the dual purpose of reducers for voltage control and a source of low wattage heat -- the more common way of reducing cost in styling dryers. In the 120 volt AC system, the heater resistance is usually connected in parallel across the motor and may be independently variable. Thus, by using plural or several differing resistance wires or variable adjustments, various wattages may be obtained all as well known. Except for the electronic control, the various adjustments are usually discrete detented points on a knob adjustment. Thus, an improved and simplified variable control for both heat and fan speed in a hair dryer is desired which control replaces complex mechanical or electronic switches and provides the "feel" of a smooth infinitely continuous adjustment of both speed and heat while, at the same time preventing an over-temperature condition by ensuring that the heat setting is never on high unless a comparable fan speed is provided for adequate cooling.